The present invention is directed to a silver-halide-containing photothermographic element for improved scanning.
It is always desirable to limit the amount of solvent or processing chemicals used in the processing of silver-halide films. A traditional photographic processing scheme for color film involves development, fixing and bleaching, and washing, each step typically involving immersion in a tank holding the necessary chemical solution. By scanning the film following printing, the subsequent processing solutions could be eliminated for the purposes of obtaining a color positive print. Instead the scanned image could be used to directly provide the color positive print.
By the use of photothermographic film, it would be possible to eliminate processing solutions altogether, or alternatively, to minimize the amount of processing solutions and the complex chemicals contained therein. A photothermographic (PTG) film by definition is a film that requires energy, typically heat, to effectuate development. A dry PTG film requires only heat; a solution-minimized PTG film may require small amounts of aqueous alkaline solution to effectuate development, which amounts may be only that required to swell the film without excess solution. Development is the process whereby silver ion is reduced to metallic silver and in a color system, a dye is created in an image-wise fashion. In all PTG films, the silver is retained in the coating after the heat development.
It can be difficult to scan through imagewise exposed and photo processed silver halide films when the undeveloped silver halide is not removed from the film during processing. The retained silver halide is reflective and this reflectivity appears as density in a scanner. The retained silver halide scatters light, decreasing sharpness and raising the overall density of the film, to the point in high silver films of making the film unsuitable for scanning. High densities result in the introduction of Poisson noise into the electronic form of the scanned image and this in turn results in decreased image quality. Furthermore, the retained silver halide can printout to ambient/viewing/scanning light, rendering non-imagewise density, degrading signal-to noise of the original scene, and raising density even higher.
Film scanners are typically designed to provide excellent electronic images from film images captured on commercially available films. In essence, the scanner systems are optimized for compatibility for current film systems. Specific areas of optimization relate to film Dmin, film Dmax and the hue of the formed dyes. Essentially all conventional camera films produce Dmin to Dmax ranges of at most 3.0 in cyan, magenta and yellow dyes. Color reversal films designed to be human viewable on projection typically have Dmins of about 0.20 or less in each color record. Color negative films designed for optical printing onto a co-designed color paper typically have red Dmins of about 0.20 or less, green Dmins of about 0.6 to about 1.0 and blue Dmins of about 0.9 to 1.5 after processing. Among the functions of photo processing is the removal of sensitizing dyes, light control densities such as the density associated with an antihalation layer or with a yellow filter layer, residual silver halide and developed silver. Conversely, photothermographic films that have limited processing can produce substantially higher densities in one or more color records precisely because the aforesaid mentioned components are not removed on photo processing. These higher densities result in poor scanning because the scanner light source is not designed to provide sufficient light to adequately illuminate the light sensitive arrays employed in scanning. This inadequate illumination results in the production of Poisson noise during scanning. There is thus a tendency to employ the minimal quantity of sensitized silver halide in photothermographic films designed for scanning. It is art recognized that conventional films typically employ quantities of sensitized silver halide sufficient to produce excellent images and that larger quantities of incorporated silver halide improve image excellence by lowering the noisiness of a formed image. Thus is thus a natural tension between the need to incorporate large quantities of sensitized silver halide to provide noise free images at capture and the need to incorporate minimal quantities of sensitized silver halide to provide noise free images at scanning.
Employing limited quantities of antihalation, Dmin adjusting and light management dyes is disclosed by Bohan et al U.S. Pat. No. 5,840,470. Employing heat clearing antihalation and light management dyes is disclosed by Ohkawa, et al., U.S. Pat. No. 6,051,359. Limiting or avoiding the use of masking couplers is disclosed by Bohan, et al., U.S. Pat. No. 5,840,470, and Sowinski, et al., U.S. Pat. No. 6,021,277. The benefit of diffuse illumination and collection is disclosed by Ishikawa, et al., U.S. Pat. No. 5,756,269 (c13 1). Fuji""s Ishikawa patent actually suggests high levels of silver halide, so that the density difference between the silver halide and reduced silver is minimized. Color correction may be the reason.
It is an object of the present invention to improve the scanning of photothermographic film without the silver halide and/or metallic silver removed.
The present invention is directed to a photothermographic element in which the density formed in a thermally processed photothermographic element is limited for the purpose of scanning the element prior to removal of silver halide, metallic silver, and/or any organic silver salts. In one embodiment of the invention, this is accomplished by employing limited quantities of sensitized silver halide in a photothermographic element.